JP4016602B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering device that determines a motor current command value to be supplied to a motor based on a steering torque detected by a torque sensor and rotationally drives the motor according to the determined motor current command value.
[0002]
[Prior art]
An electric power steering device installed in a vehicle assists the steering force of the vehicle with a motor. This is because a steering torque applied to a steering wheel is applied to a steering mechanism in which the steering wheel is connected via a steering shaft. A torque sensor to be detected and a motor for assisting the operation of the steering mechanism are provided, and the motor is driven in accordance with the steering torque detected by the torque sensor, thereby reducing the operating force on the steered wheels.
[0003]
When the steering assist motor used in the electric power steering apparatus is, for example, a brushless motor, the characteristic is that the larger the applied voltage, the higher the rotational speed, but the maximum value of the rotational torque determined by the current that flows. Is constant regardless of the voltage, and the larger the applied voltage, the faster the rotation with the same rotational torque.
[0004]
The steering assist motor is driven by an in-vehicle battery, and the voltage fluctuation of the in-vehicle battery is assumed to be, for example, 10 to 16V. The steering assist motor is designed to meet the expected minimum voltage (10V) in consideration of the voltage fluctuation of the on-board battery, so it is a low-voltage, high-current motor. There is a problem that it is larger than that designed for high voltage.
Therefore, in the Japanese Patent Application No. 12-76928, the present applicant can supply a stable steering assist force to the steering assist motor even when the voltage of the in-vehicle battery fluctuates. An electric power steering apparatus that can further reduce the size of a steering assist motor has been proposed.
[0005]
[Problems to be solved by the invention]
In the electric power steering apparatus according to the above proposal, a boost chopper circuit that boosts the voltage of the on-vehicle battery is used to supply a voltage at which a stable steering assist force is always obtained. However, the boost chopper circuit has a constant frequency. Therefore, there is a problem that electromagnetic noise, particularly audible electromagnetic noise is easily generated.
The present invention has been made in view of the above-described circumstances, and can provide a steering assist motor with a voltage that always provides a stable steering assist force even when the voltage of the in-vehicle battery fluctuates. An object of the present invention is to provide an electric power steering apparatus that can further reduce the size of a motor for assisting steering and can reduce the influence of electromagnetic noise caused by a boost chopper circuit.
[0006]
[Means for Solving the Problems]
An electric power steering apparatus according to a first aspect of the present invention includes a torque sensor that detects a steering torque applied to a steered wheel, and a steering assist motor that is driven by a drive circuit to which an in-vehicle battery voltage is applied, and is detected by the torque sensor. In the electric power steering apparatus in which a motor current command value to be passed to the motor is determined based on the steering torque, and the drive circuit rotates the motor according to the determined motor current command value, whether or not the output of the motor is insufficient A first determination unit that determines whether the first determination unit is insufficient, a boost command unit that outputs a boost command for boosting the battery voltage, and an output from the boost command unit Boosting chopper circuit that boosts the battery voltage according to the boosting command, and the influence of electromagnetic noise by the boosting chopper circuit In order to reduce, and PFM control means operating frequency of the boost chopper circuit is changed, and a detection means for detecting a voltage applied to the drive circuit, the PFM control means constant boosted voltage In order to maintain, the boost chopper circuit is configured to be controlled based on a detection value of the detection means .
[0007]
In this electric power steering apparatus, the torque sensor detects the steering torque applied to the steered wheels, and the steering assist motor is driven by a drive circuit to which a vehicle-mounted battery voltage is applied. A motor current command value to be passed to the motor is determined based on the steering torque detected by the torque sensor, and the drive circuit drives the motor to rotate in accordance with the determined motor current command value. The first determination means determines whether or not the output of the motor is insufficient. When it is determined that the output is insufficient, the boost command means outputs a boost command for boosting the output voltage of the in-vehicle battery. . The boost chopper circuit boosts the vehicle-mounted battery by changing the operating frequency of the boost chopper circuit in order to reduce the influence of electromagnetic noise by the boost chopper circuit by the boost command output.
[0008]
In the PFM control, the duty ratio is controlled by changing the number of pulses (pulse density; constant pulse width) within a fixed time, and the voltage boost amount of the boost chopper circuit is controlled by the duty ratio. At the time of boosting, the duty ratio is controlled so that the applied voltage applied to the drive circuit is detected and maintained at a constant value. The detection means detects the voltage applied to the drive circuit, and the PFM control means controls the operation of the boost chopper circuit based on the detection value of the detection means so as to keep the boosted voltage constant.
[0009]
As a result, even when the voltage of the in-vehicle battery fluctuates, a voltage capable of always obtaining a stable steering assist force can be supplied to the steering assist motor, and the size of the steering assist motor can be further reduced. At the same time, the electromagnetic noise generated by the step-up chopper circuit is converted into white noise as a result, and an electric power steering apparatus that can reduce the influence of the electromagnetic noise can be realized.
[0010]
According to a second aspect of the present invention, there is provided an electric power steering apparatus according to the second aspect of the present invention, wherein a second determination unit that determines whether the output of the motor is excessive when the boost chopper circuit boosts the battery voltage; A step-down command unit that outputs a step-down command when the determination unit determines that the step-down command is excessive, and the step-up chopper circuit stops boosting the battery voltage by the step-down command output by the step-down command unit; Features.
[0011]
In this electric power steering device, when the boost chopper circuit is boosting the battery voltage, the second determination means determines whether the output of the motor is excessive, and the second determination means is excessive. When the determination is made, the step-down command means outputs a step-down command for stepping down the voltage, and the step-up command causes the boost chopper circuit to stop boosting the battery voltage, so that the in-vehicle battery voltage applied to the drive circuit is boosted. When it is no longer necessary, the pressure can be reduced, and when a large steering assist force is no longer needed, the vehicle battery voltage can be supplied to the steering assist motor without increasing the pressure, and the steering assist motor is mounted on the vehicle. It is possible to realize an electric power steering device that can prevent a decrease in efficiency due to boosting of the battery voltage.
[0014]
In the electric power steering apparatus according to a third aspect of the invention, the motor current command value is a duty ratio for PWM control of the motor, and the drive circuit rotationally drives the motor by PWM control based on the duty ratio. It is characterized by doing.
In this electric power steering apparatus, the motor current command value is a duty ratio for PWM control of the motor, and the drive circuit rotates the motor by PWM control based on this duty ratio, so the vehicle battery voltage fluctuates. Even so, it is possible to supply an electric power steering device that can supply a stable steering assist force voltage to the steering assist motor and can further reduce the size of the steering assist motor. I can do it.
[0015]
In the electric power steering apparatus according to a fourth aspect of the present invention, the first determination means determines that the output of the motor is insufficient when the duty ratio is greater than 90%, and the second determination means When the ratio is smaller than 50%, the motor output is determined to be excessive.
In this electric power steering apparatus, the first determination means determines that the motor output is insufficient when the duty ratio for PWM control of the motor is greater than 90%, and the second determination means determines that the duty ratio is When it is less than 50%, it is determined that the output of the motor is excessive. Therefore, even when the on-vehicle battery voltage fluctuates, a voltage that always provides a stable steering assist force can be supplied to the steering assist motor. An electric power steering apparatus that can further reduce the size of the steering assist motor can be realized.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings showing embodiments thereof.
FIG. 1 is a block diagram showing a main configuration of an embodiment of an electric power steering apparatus according to the present invention. In this electric power steering apparatus, a torque detection signal detected and output by a torque sensor 10 for detecting torque applied to a steering shaft (not shown) is supplied to a microcomputer 12 via an interface circuit 11 to thereby control the vehicle speed. A vehicle speed signal detected and output by the detected vehicle speed sensor 20 is given to the microcomputer 12 via the interface circuit 21.
[0017]
A relay control signal output from the microcomputer 12 is input to the relay drive circuit 15, and the relay drive circuit 15 turns the fail-safe relay contact 15a on or off according to the relay control signal.
The clutch control signal output from the microcomputer 12 is input to the clutch drive circuit 16, and the clutch drive circuit 16 turns the clutch 19 on or off according to the clutch control signal. The drive power for the clutch 19 is supplied from the terminal on the motor drive circuit 13c side of the fail-safe relay contact 15a.
[0018]
The microcomputer 12 creates a motor current command value (PWM command value) by referring to a torque / current table 18a in the memory 18 based on a torque detection signal, a vehicle speed signal, and a motor current signal described later. The motor current command value is given to the motor drive circuit 13c. The motor drive circuit 13c is applied with the power supply voltage of the in-vehicle battery P through the fail-safe relay contact 15a, and rotates the brushless motor 24, which is a steering assist motor, based on the given motor current command value.
[0019]
When the brushless motor 24 rotates, the rotor position detector 14 detects the rotor position, and the motor drive circuit 13c controls the rotation of the brushless motor 24 based on the detected rotor position signal.
The motor current flowing through the brushless motor 24 is detected by the motor current detection circuit 17 and is given to the microcomputer 12 as a motor current signal.
[0020]
FIG. 2 is a block diagram showing the configuration of the brushless motor 24, the motor drive circuit 13c, and the motor current detection circuit 17. The brushless motor 24 includes a stator 24a in which coils A, B, and C are star-connected, a rotor (rotor) 24b that is rotated by a rotating magnetic field generated by the coils A, B, and C, and a rotational position of the rotor 24b. And a rotor position detector 14 for detecting.
[0021]
In the motor drive circuit 13c, the power supply voltage of the in-vehicle battery P is applied to the anode of the diode D7 through the coil L, and the cathode of the diode D7 is connected to the positive terminal of the switching circuit 8b. The transistor Q7 is connected between the anode of the diode D7 and the ground terminal, and the diode D8 is parasitic between the source and drain of the transistor Q7. A smoothing capacitor C1 is connected between the cathode of the diode D7 and the ground terminal, and a circuit voltage detection circuit 26 for detecting the voltage across the smoothing capacitor C1 is connected to both terminals of the smoothing capacitor C1. The voltage detection output from the circuit voltage detection circuit 26 is given to the microcomputer 12.
[0022]
A PFM circuit 28 (PFM control means) that generates and outputs a PFM (Pulse Frequency Modulation) signal based on a step-up / step-down command (step-up / step-down command) given from the microcomputer 12 is connected to the gate of the transistor Q7. ing.
The coil L, the diode D7, the smoothing capacitor C1, the transistor Q7, and the PFM circuit 28 described above constitute a boost chopper circuit 8f.
[0023]
A resistor R1 and a Zener diode ZD are connected in series between the positive electrode terminal and the negative electrode terminal of the smoothing capacitor C1, and one node of the resistor R1 and the cathode node of the Zener diode ZD are connected to the other terminal of the resistor R1. Between, a series circuit of resistors R3 and R2 is connected. The connection point of the resistors R3 and R2 is connected to the base of the PNP transistor Q8 (switching element), and the resistors R3 and R2 are a bias circuit for the transistor Q8.
The emitter of the transistor Q8 is connected to the other terminal of the resistor R1, and the collector is connected to the anode of the diode D7.
[0024]
In the switching circuit 8b, transistors Q1 and Q2 connected in series between the positive terminal and the ground terminal and diodes D1 and D2 connected in series in the opposite direction are connected in parallel, and transistors Q3 and Q4 connected in series. The diodes D3 and D4 connected in series in the reverse direction are connected in parallel, and the transistors Q5 and Q6 connected in series and the diodes D5 and D6 connected in series in the reverse direction are connected in parallel.
[0025]
The other terminal U of the star-connected coil A is connected to the common connection node of the transistors Q1 and Q2 and the common connection node of the diodes D1 and D2, and the common connection node of the transistors Q3 and Q4 and the diode D3 The other terminal V of the coil B that is star-connected is connected to the common connection node of D4, and star-connected to the common connection node of the transistors Q5 and Q6 and the common connection node of the diodes D5 and D6. The other terminal W of the coil C is connected.
[0026]
The rotational position of the rotor 24b detected by the rotor position detector 14 is notified to the gate control circuit 8c. The rotation direction and the motor current command value (PWM command value) are given from the microcomputer 12 to the gate control circuit 8c. The gate control circuit 8c turns on / off the gates of the transistors Q1 to Q6 in accordance with the direction of rotation and the rotation position of the rotor 24b, for example, U-V, U-W, V-W, V Like -U, W-U, W-V, and U-V, the path of the current flowing through the stator 24a is switched to generate a rotating magnetic field.
[0027]
The rotor 24b is a permanent magnet, and rotates by receiving a rotational force from the rotating magnetic field. The gate control circuit 8c also controls increase / decrease of the rotational torque of the brushless motor 24 by PWM (Pulse Width Modulation) control of on / off of the transistors Q1 to Q6 according to the motor current command value.
The diodes D1 to D6 are for absorbing noise generated by turning on / off the transistors Q1 to Q6.
The motor current detection circuit 17 detects and adds currents flowing through the terminals U, V, and W of the brushless motor 24, and gives the result to the microcomputer 12 as a motor current signal.
[0028]
Hereinafter, the operation of the electric power steering apparatus having such a configuration will be described with reference to the flowchart of FIG.
In the steering assist operation, the microcomputer 12 first reads the torque detection signal detected by the torque sensor 10 via the interface circuit 11 (S2), and then the vehicle speed signal detected by the vehicle speed sensor 20 via the interface circuit 21. (S4).
The microcomputer 12 determines the target motor current with reference to the torque / current table 18a from the read (S4) vehicle speed signal and the read (S2) torque detection signal (S6).
[0029]
Next, the microcomputer 12 reads the motor current signal from the motor current detection circuit 17 (S8), determines (S6) the difference between the determined target motor current and the read (S8) motor current signal (S10), Based on the calculated difference, a motor current command value is determined so that the target motor current flows through the brushless motor 24 (S12).
[0030]
Next, the microcomputer 12 determines (S12) the determined PWM command value and rotation direction according to the motor current command value (S14), and sends the determined PWM command value and rotation direction instruction signal to the motor drive circuit 13c. At the same time (S16), based on the PWM command value, an operation for stepping up or down the voltage applied to the switching circuit 8b of the motor drive circuit 13c is performed (S18), and the process returns to other processing.
The motor drive circuit 13c rotates the brushless motor 24 based on the given PWM command value and the rotation direction instruction signal.
[0031]
FIG. 4 is a flowchart showing the operation (S18) for boosting or stepping down the voltage applied to the switching circuit 8b described above.
First, the microcomputer 12 determines whether or not the flag F = 1 (S20). If the flag F is not 1, the microcomputer 12 determines (S14 in FIG. 3) whether or not the PWM command value is greater than 90%. Then, it is determined whether or not the output of the brushless motor 24 is insufficient (S22).
[0032]
When the power supply voltage of the on-vehicle battery P to be applied is 12 V, for example, the switching circuit 8 b performs an on / off operation according to the PWM command value so that the voltage actually applied to the brushless motor 24 (average voltage) ) And a target motor current is caused to flow through the brushless motor 24.
Therefore, when the PWM command value is 90%, the voltage (average voltage) actually applied to the brushless motor 24 is actually when the PWM command value is 100%, as shown in FIG. It is lower than 12V applied to.
[0033]
When the determined PWM command value is larger than 90% (S22), the microcomputer 12 determines that the output of the brushless motor 24 is insufficient and gives a boost command to the PFM circuit 28 (S24). The flag F is set to 1 (S26).
When the boost command is given, the PFM circuit 28 turns on / off the transistor Q7 by the PFM signal to operate the boost chopper circuit 8f, and the voltage applied to the switching circuit 8b is, for example, as shown in FIG. , Boost to 16V.
[0034]
When boosting to 16V, the microcomputer 12 (PFM control means) controls the PFM circuit 28 so as to maintain 16V by a boost command using the voltage detection signal from the circuit voltage detection circuit 26 as a feedback signal.
Since the voltage applied to the motor drive circuit 13c fluctuates due to a change in the vehicle battery voltage or a change in the motor current, the duty ratio of the PFM circuit is controlled to keep the applied voltage after boosting constant.
[0035]
When the microcomputer 12 determines that the determined PWM command value is smaller than 90% (S22) and the output of the brushless motor 24 is not insufficient, the microcomputer 12 returns to the steering assist operation.
The microcomputer 12 performs the steering assist operation shown in the flowchart of FIG. 3 when the boost chopper circuit 8f operates and boosts the voltage to be applied to the switching circuit 8b, as in the case of not boosting the voltage.
[0036]
When the flag F = 1 (S20), the microcomputer 12 determines that the voltage applied to the switching circuit 8b is boosted to 16V as shown in FIG. 5B (FIG. 5). 3S14) It is determined whether the PWM command value is smaller than 50%, that is, whether the output of the brushless motor 24 is excessive (S28).
When the microcomputer 12 determines (S14 in FIG. 3) that the PWM command value is less than 50% and the output of the brushless motor 24 is excessive (S28) (the voltage actually applied to the brushless motor 24 ( The average voltage is lower than 12V), a step-down command is given to the PFM circuit 28 (S30), and the flag F is set to 0 (S32).
[0037]
When the step-down command is given, the PFM circuit 28 stops the operation of the step-up chopper circuit 8f and restores the voltage applied to the switching circuit 8b to 12V as shown in FIG.
When the microcomputer 12 determines that the determined PWM command value is greater than 50% (S28) and the output of the brushless motor 24 is not excessive, the microcomputer 12 returns to the steering assist operation.
[0038]
During each operation described above, the power generated by the brushless motor 24 is increased by returning the steering wheel (steering wheel), the voltage applied to the switching circuit 8b is increased, and the Zener voltage of the Zener diode ZD (for example, 18V) is set. ), The Zener diode ZD is turned on, and a current I ′ flows through the resistor R1. As a result, the bias voltage to the base of the transistor Q8 by the resistors R3 and R2 becomes lower than the emitter voltage of the transistor Q8, the transistor Q8 is turned on, and the current I is passed from the switching circuit 8b to the vehicle battery P through the coil L. Refluxed.
[0039]
When the current I is circulated from the switching circuit 8b to the in-vehicle battery P and the voltage applied to the switching circuit 8b drops and becomes lower than the Zener voltage of the Zener diode ZD, the Zener diode ZD is turned off and the transistor Q8 is also turned off. Become.
When the voltage applied to the switching circuit 8b is increased by the power generated by the brushless motor 24, the Zener diode ZD and the transistor Q8 are repeatedly turned on / off by the above-described operation, and greatly exceed the Zener voltage of the Zener diode ZD. There is no.
[0040]
As the motor current command value, the duty ratio is changed by the PWM method for modulating the voltage application pulse width. Specifically, the motor current command value is output as a PWM command value to control the auxiliary force of the motor.
For example, in the case of a sine wave approximation PWM type synchronous system that compares a sine wave and a triangular wave, the duty ratio (PWM value) between half wavelengths of the sine wave is the motor current command value. In this embodiment, the brushless motor is described. However, it is needless to say that the present invention can be applied to a motor other than the brushless motor.
[0041]
【The invention's effect】
According to the electric power steering apparatus according to the first shot bright, even if the output voltage of the mounted battery fluctuates, it can always supply a voltage from which a stable steering assisting force is obtained to the motor for steering assist, the steering assist Therefore, it is possible to realize an electric power steering apparatus that can further reduce the size of the motor for use and reduce electromagnetic wave noise due to the boost chopper circuit to white noise.
[0042]
According to the electric power steering device of the second aspect of the present invention, when the output voltage of the in-vehicle battery applied to the drive circuit is not required to be increased, the output voltage can be decreased, and when the large steering assist force is not required, the voltage is increased. Therefore, it is possible to provide an electric power steering device that can supply a vehicle-mounted battery voltage to a steering assist motor and prevent a decrease in efficiency due to a boost in the output voltage of the vehicle-mounted battery of the steering assist motor. .
[0043]
According to the third and fourth aspects of the electric power steering apparatus, even when the output voltage of the vehicle-mounted battery fluctuates, a voltage that always provides a stable steering assist force can be supplied to the steering assist motor. An electric power steering apparatus that can further reduce the size of the auxiliary motor can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a main configuration of an electric power steering apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram showing configurations of a brushless motor, a motor drive circuit, and a motor current detection circuit.
FIG. 3 is a flowchart showing an operation of the electric power steering apparatus shown in FIG. 1;
FIG. 4 is a flowchart showing an operation for stepping up or stepping down a voltage applied to a switching circuit.
FIG. 5 is an explanatory diagram for explaining the operation of the electric power steering apparatus according to the present invention.
[Explanation of symbols]
8b Switching circuit 8c Gate control circuit 8f Boost chopper circuit 10 Torque sensor 12 Microcomputer (PFM control means)
13c Motor drive circuit 17 Motor current detection circuit 18a Torque / current table 24 Brushless motor (steering assist motor)
28 PFM circuit (PFM control means)
26 Circuit voltage detection circuit (detection means)
P On-board battery C1 Smoothing capacitor F Flag L Coil Q7 Transistor Q8 Transistors R1, R2, R3 Resistor ZD Zener diode

Claims (4)

A motor to be supplied to the motor based on the steering torque detected by the torque sensor, comprising: a torque sensor for detecting a steering torque applied to the steering wheel; and a steering assist motor driven by a drive circuit to which an in-vehicle battery voltage is applied. In the electric power steering apparatus in which a current command value is determined, and the drive circuit rotates the motor according to the determined motor current command value.
A first determination unit that determines whether or not the output of the motor is insufficient; and a booster that outputs a boost command for boosting the battery voltage when it is determined that the first determination unit is insufficient The operating frequency of the step-up chopper circuit varies in order to reduce the influence of electromagnetic noise caused by the command means, the step-up chopper circuit that boosts the battery voltage, and the step-up chopper circuit. PFM control means for detecting the voltage applied to the drive circuit, and the PFM control means is based on the detection value of the detection means to keep the boosted voltage constant. An electric power steering device configured to control the operation of the step-up chopper circuit .   When the boost chopper circuit boosts the battery voltage, the second determination means for determining whether or not the output of the motor is excessive; and when the second determination means determines that the output is excessive 2. The electric power steering apparatus according to claim 1, further comprising a step-down command means for outputting a step-down command, wherein the step-up chopper circuit stops boosting the battery voltage by the step-down command output by the step-down command means. 3. The electric power steering according to claim 1, wherein the motor current command value is a duty ratio for PWM control of the motor, and the drive circuit rotationally drives the motor by PWM control based on the duty ratio. apparatus. The first determination means determines that the output of the motor is insufficient when the duty ratio is greater than 90%, and the second determination means determines that the motor output is less than 50% when the duty ratio is less than 50%. 4. The electric power steering apparatus according to claim 3, wherein the electric power steering apparatus is configured to determine that the output is excessive.

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